The center of the Universe

[nimbus]

Flatearth is just trolling.

 

[SpeedFreek]

I am inclined to agree with you. This thread seems destined to end up in the unexplained forum.

 

[MeteorWayne]

Now that it is no longer on the SDC front page, a major housecleaning will occur shortly. Those posts related to the original subject will remain. The rest will find a new home.

 

[Jerromy]

Perhaps this comment can stay since it is relevant and provokes logical thought.

I need to vent after all the arguing I've read here so I'm going to split some hairs.

To say that the surface of a sphere whether a finite size or an infinite size has a center "on the surface" is impossible. To say there is an opposite to any given point is obvious.

To say that the universe could be like an old atari 2600 tank game where the tanks could go off one edge of the screen and appear on the other would say that stars could been seen at opposite points of view from opposite sides, for stars at half way "around" the universe they should look the same.

To say that the expansion of the universe is accelerating simply because what we see the further we look appears to support that assumption means that we need to look more closely at closer objects to figure out what we REALLY see out there.

I feel there is a center to the universe even though it has no boundaries. Everything revolves around something.

 

[mabus]

To say that the surface of a sphere whether a finite size or an infinite size has a center "on the surface" is impossible. To say there is an opposite to any given point is obvious.

To say that the universe could be like an old atari 2600 tank game where the tanks could go off one edge of the screen and appear on the other would say that stars could been seen at opposite points of view from opposite sides, for stars at half way "around" the universe they should look the same.

To say that the expansion of the universe is accelerating simply because what we see the further we look appears to support that assumption means that we need to look more closely at closer objects to figure out what we REALLY see out there.

I feel there is a center to the universe even though it has no boundaries. Everything revolves around something.

A couple of points here. You're right about the "surface" comment. Relativity teaches us that we are 3 dimensional beings who are observing a universe that is more than 3 dimensions. If string theory is correct it could be as many as 11 dimensions. It just may be that we cannot percieve "up" in such a way as to be able to percieve any theoretical "center".

We say that the expansion of the universe appears to be accellerating because, the objects we observe appear to be going faster than they were going back in time. We do not yet know why this is the case, but it is what we have observed.

Something with no bounderies cannot have a center. Think about it logically... a center is the middle from one boundery to another, the midway point between two bounderies, If it has no "end" there is nothing to measure a center FROM. Imagine an ocean that never ends, no surface, no shore, no bottom. What's the center of that? For all practical intents and purposes it may very well have an undefined unpercieved unobserved unknown center. If so we'd never know about it. The moment you say the universe has no bounderies, the conclusion that it must have no center follows logically.

 

[SpeedFreek]

To say that the universe could be like an old atari 2600 tank game where the tanks could go off one edge of the screen and appear on the other would say that stars could been seen at opposite points of view from opposite sides, for stars at half way "around" the universe they should look the same.

You are right in that, if the universe had such a topology, we could in theory see the same distant galaxies in different directions, but that is only if light has had time to travel "all the way around" the universe. If the universe were small enough to let light "circumnavigate" it, we could find observational evidence for this via repeated patterns in the CMBR, and we have looked!

Unfortunately, it seems as if the fundamental domain of the universe is at least as large as our observable part of it, so our universe is too large for us to be able to find this observational evidence. So, whilst this is still a possible shape for the universe, we know of no way to confirm it as of yet.

See Extending the WMAP Bound on the Size of the Universe

Clues to the shape of our Universe can be found by searching the CMB for matching circles of temperature patterns. A full sky search of the CMB, mapped extremely accurately by NASA's WMAP satellite, returned no detection of such matching circles and placed a lower bound on the size of the Universe at 24 Gpc. This lower bound can be extended by optimally filtering the WMAP power spectrum. More stringent bounds can be placed on specific candidate topologies by using a a combination statistic. We use optimal filtering and the combination statistic to rule out the infamous "soccer ball universe'' model.

(The "soccer ball" universe is one of the possible topologies, otherwise known as the Poincare dodecahedral space)

As for the acceleration of the expansion, it was our observations of Type 1a supernovae, over a range of distances, that showed us that the rate of expansion was accelerating. The closer we looked, the further away these supernovae were, when compared to where they should have been if the expansion were still slowing.

The expansion of the universe means that the further away an object is, the faster it apparently recedes. The acceleration of that expansion means the closer objects are receding a little faster than they should be when compared to the more distant ones, but recession speed still increases with distance. The key point is whether the relationship is linear or not.

 

[Jerromy]

The expansion of the universe means that the further away an object is, the faster it apparently recedes. The acceleration of that expansion means the closer objects are receding a little faster than they should be when compared to the more distant ones, but recession speed still increases with distance. The key point is whether the relationship is linear or not.

So I take this as The Milky Way and The Andreomeda galaxies are witness to the non-local phenomena involving accelerated recession of supernovae which is apparently more noticable at closer ranges due to the optical lag of distance. It makes sense why it is believed to be the result of space expanding since the further the distance the greater the rate of recession. It also makes sense that the closer the supernova the sooner we would see the distance accelerate, while very distant supernovae would be receding at the supposed equal acceleration but we would have to account for the delay in witnessing it as light seems to be "immune" to the expansion as per velocity. What we see a supernova doing a million light years away is what it did a million years ago, what we see a supernova doing a thousand light years away happened 1000 years ago and it seems to be further away per expected location than the million light year supernova? I know supernovae are rare but I still feel an inconsistency of logic is in there somewhere... let me ponder on this a bit...

 

[Jerromy]

I'm a little confused here... type 1A supernovae have an expected luminosity which decreases with distance as the emitted photons would be dispersed further over greater distances, that I understand. How then could a rare and rather unpredictable occurance be used to define a supposed distance which is otherwise undefined to compare where the star was that exploded? It seems like it is assumed where a supernova should occur and since it occurs at a greater distance than expected then it must have receeded further than typical expansion would place it.

 

[FlatEarth]

So stop talking about the state of space and time "before" the Big Bang, then.

Maybe it is you who should stop talking about how I can’t talk about it.

You are incorrect. It has been known that the whole universe might be infinite within BB theory for decades. Only the observable universe is known to be finite, by definition. You obviously don't understand the theory properly if you think those illustrations are wrong.

I strongly disagree with you, and in my opinion you have adopted or were taught incorrect information. The universe includes everything, and the BB theory is about the universe. Go ahead and believe in a bigger universe. There is absolutely no evidence to support it.

http://www.umich.edu/~gs265/bigbang.htm

http://www.big-bang-theory.com/

How can you picture a model with intrinsic curvature, from the outside? Can you picture 4 dimensional spaces then?

An unbounded sphere is still a sphere. The 3D environment within the sphere is continuous and appears infinite, but the volume within the sphere itself is finite. That is how I picture it, and yes I do believe this is the shape of the universe. That is my opinion, and is how I decided there is a center. The center is undetectable inside the sphere, but it does exist when considering the overall shape.

I see that you are now changing your position, in fact you have completely reversed it. Now you say the universe is bounded. I am guessing this is because you didn't actually know what unbounded meant until we explained it to you.

So, you sould realize by now that I did not change my position. I tend to mess with people who mess with me.

That link has no place in the physics forum, it is full of errors, misconceptions and biased interpretations.

And this leads me to believe you have no sense of humor.

 

[ssnozenoszka]

So I guess that there are 2 possible conclusions; there is no center to the universe or we are the center of the universe. I think it is pretty clear that it is the former not the latter. There is much more evidence that the universe has no center point but this analysis is the most straight forward, I believe. Visit this site and take a look at the graphic on expansion it is quite good.

Hey Origin, thanks for your reply.

For me there are 2 possible conclusions. Either every point is the center or there is a true center. The website you sent with the points doesnt really prove anything one way or the other. It would be really nice if we had astro images of the universe taken a million years ago, that would surely help. But no monkey has ever made a telescope, let alone a CCD device.

I like to go from simple to complex in explanations for things. And I just don't yet see a real justification for the complexity of our explanations of the universe.

Imagine a pingpongball in a vacuum filled evenly with a highly compressed gas. The size of the pingpongball starts growing to the size of a basketball through to a skippy ball. While the pingpongball grows, all single smallest units of space expand equally. At one point the gas condenses into matter in the skippy ball, which continues to expand.

Besides the fact that all matter is moving away from all other matter because of the expansion, its still a skippy ball so there will still be a center of gravity towards which all matter is drawn in some way (the middle of the ball). If our observable universe is just a pingpong ball inside of the skippy ball what would we see around us? I think we would see exactly what we see now.

The effect of the expansion is just so dominant that it masks the effects of gravity within the hypothetical skippy ball. And because we see only a small fraction of it it makes us think that the universe is infinite and has no center.

It wasn't untill we looked at the sun when the moon was exactly in front of it, that we started to learn more about the sun and its inner workings. In this case I think we need to try to look at (dont ask me how) the observable universe without the effect of expansion of space. Would it still be exactly the same in all directions?

We don't know. Observations and theories just aren't reliable enough yet.

Please people direct me to real evidence and real solid observations that prove there is no center. Show me why science accepted this so broadly. I'm not trying to be rebellious, just eager to understand.

Kind regards,

S

 

[origin]

We have lots of pictures of the way the universe looked 1 million years ago.

I would venture a guess that with the cold front that just went through my neck of the woods and since I live in the country (with excellent viewing conditions) that I will be able to look at a spot very close to Pegasus and will be able to see the universe as it looked about 2.5 million years ago. It will be kinda fuzzy though....

 

[mabus]

You are incorrect. It has been known that the whole universe might be infinite within BB theory for decades. Only the observable universe is known to be finite, by definition. You obviously don't understand the theory properly if you think those illustrations are wrong.

I strongly disagree with you, and in my opinion you have adopted or were taught incorrect information. The universe includes everything, and the BB theory is about the universe. Go ahead and believe in a bigger universe. There is absolutely no evidence to support it.

http://www.umich.edu/~gs265/bigbang.htm

http://www.big-bang-theory.com/

The first page you cited has a number of glaring errors. I just barely glanced at it and immediately caught two huge ones.

About 15 billion years ago a tremendous explosion started the expansion of the universe. This explosion is known as the Big Bang.

Of course the Big Bang wasn't an explosion at all.

your second page disagrees with the first one saying...

There are many misconceptions surrounding the Big Bang theory. For example, we tend to imagine a giant explosion. Experts however say that there was no explosion;

The other error I spotted just glancing at the page was

The origin of the Big Bang theory can be credited to Edwin Hubble. Hubble made the observation that the universe is continuously expanding.

Actually the origin of the theory is due to Georges Lemaitre. Hubble merely provided the first observational evidence of the predicted expansion.

The second page also over reaches when it claims our universe is known to have certainly had a beggining, and that it "sprang into existence as a singularity". We know no such thing. There is not a single piece of empirical evidence of such a claim. The only testable evidence we have is that the universe existed as an expanding area of space-time. We reach the conclusion that it was once a singularity for purely mathematical reasons (the same basis you utterly reject all other models by the way).

How can you picture a model with intrinsic curvature, from the outside? Can you picture 4 dimensional spaces then?

An unbounded sphere is still a sphere. The 3D environment within the sphere is continuous and appears infinite, but the volume within the sphere itself is finite. That is how I picture it, and yes I do believe this is the shape of the universe. That is my opinion, and is how I decided there is a center. The center is undetectable inside the sphere, but it does exist when considering the overall shape.

That of course assumes that the universe is in fact finite. What if it's infinite, but expanding in our local area and contracting in others? Like waves rolling up and down on a vast infinite ocean. The fact is we don't know whether the universe is finite or infinite. All we can say is that the observeable part of it we can see around us is expanding. Anything beyond that is over reaching.

That link has no place in the physics forum, it is full of errors, misconceptions and biased interpretations.

And this leads me to believe you have no sense of humor.

I doubt that was a joke, I think you just got caught with your pants down and couldn't bring yourself to admit the error, but that's fine. You still need to show us a link to a legitimate scientific source claiming the universe has a center that is not a joke then.

 

[origin]

We don't know. Observations and theories just aren't reliable enough yet.

Please people direct me to real evidence and real solid observations that prove there is no center. Show me why science accepted this so broadly. I'm not trying to be rebellious, just eager to understand.

Kind regards,

S

No you are just being a contrarian. There are hundreds of sites on the internet that duscuss astronomy. Your library is full of books on astronomy. You local community college probably has astronomy courses. If you are truly eager to understand then use these resources. I do not feel like presenting evidence and have you disregared it. You state clearly in the first sentence that your mind is made up. Why waste my time?

 

[FlatEarth]

http://www.umich.edu/~gs265/bigbang.htm
http://www.big-bang-theory.com/

The first page you cited has a number of glaring errors. I just barely glanced at it and immediately caught two huge ones.

About 15 billion years ago a tremendous explosion started the expansion of the universe. This explosion is known as the Big Bang.

Of course the Big Bang wasn't an explosion at all.
your second page disagrees with the first one saying...

There are many misconceptions surrounding the Big Bang theory. For example, we tend to imagine a giant explosion. Experts however say that there was no explosion;

The other error I spotted just glancing at the page was

The origin of the Big Bang theory can be credited to Edwin Hubble. Hubble made the observation that the universe is continuously expanding.

Actually the origin of the theory is due to Georges Lemaitre. Hubble merely provided the first observational evidence of the predicted expansion.
The second page also over reaches when it claims our universe is known to have certainly had a beggining, and that it "sprang into existence as a singularity". We know no such thing. There is not a single piece of empirical evidence of such a claim. The only testable evidence we have is that the universe existed as an expanding area of space-time. We reach the conclusion that it was once a singularity for purely mathematical reasons (the same basis you utterly reject all other models by the way).

Your criticisms of both articles do not invalidate them. Sometimes the BB is referred to as an explosion because of its violent nature, but we all know it was a violent expansion. The writer of the article no doubt understands the difference. The article also states Hubble made the observation, so in that sense he did have responsibility. This is pointless nitpicking.

That of course assumes that the universe is in fact finite. What if it's infinite, but expanding in our local area and contracting in others? Like waves rolling up and down on a vast infinite ocean. The fact is we don't know whether the universe is finite or infinite. All we can say is that the observeable part of it we can see around us is expanding. Anything beyond that is over reaching.

It may or may not be infinite, but my premise is based on a theory that says certain things that lead me to make my conclusions. As I have said repeatedly, there is room to make other conclusions and it is up to the individual to decide what to believe. Some may choose to say they can't decide because the evidence is incomplete, or that there is no center because they believe in an infinite universe, or that they believe in an expanding spherically shaped universe with certain properties (bingo!). They are just opinions, and not completely based on evidence. It comes down to how far you want to rely on the collective imagination of others to base your conclusions. I am sticking as closely as I can to the evidence we can observe and to a theory based on that evidence. My leap of faith is smaller than many other ideas, such as the one you made.

And this leads me to believe you have no sense of humor.

I doubt that was a joke, I think you just got caught with your pants down and couldn't bring yourself to admit the error, but that's fine. You still need to show us a link to a legitimate scientific source claiming the universe has a center that is not a joke then.

Two peas in a pod, you and SF.
A universe with a center is not a popular notion, but it cannot be ruled out. As I mentioned in an earlier post, I believe the popularization of the "no center" belief originated from the desire to establish that the BB was not an explosion that radially expelled matter, but rather was the homogeneous expansion of the universe from a single point. It quickly evolved into the widely held belief that there is no center. There is safety in following the pack, and the scientific community is not immune. This behavior is most certainly evident in this forum.
Here is an article about Lemaître that you should find enlightening.

http://math.ucr.edu/home/baez/physics/R ... entre.html

 

[SpeedFreek]

I recognise that link FlatEarth, it is the one I posted earlier in this thread, and it supports my position!

Of course there are many other even less uniform shapes the universe could have, with or without an identifiable centre. If it turned out to have a centre on some scale beyond the observable universe, such a centre might turn out to be just one of many "centres" on much larger scales, just as the centre of our galaxy did before.

In other words, although the standard Big Bang models describe an expanding universe with no centre, and this is consistent with all observations, there is still a possibility that these models are not accurate on scales larger than we can observe. We still have no real answer to the question "Where is the centre of the universe?".

Well, this is a turnaround and a half! If you agree with that link, you are now the one relying on theoretical ideas beyond our observable universe in order to justify the notion of the universe having a centre, whereas the standard Big Bang model (the FLRW universe I mentioned earlier) says there is no centre!

So, standard Big Bang models have a universe with no centre, but if you want to speculate on scales larger than our observable universe you might find a centre. But there is a caveat here - as the link says:

"If it turned out to have a centre on some scale beyond the observable universe, such a centre might turn out to be just one of many "centres""

:roll:

Are you now speculating outside the standard BB models and outside of the observable universe? If so, this is exactly what you accused me of earlier in this thread.

As far as I am aware, the LTB model does have conflicts with the cosmological principle, (i.e it is not homogeneous) which is why there isn't a lot of support for it (aside from the fact that it is untestable, just like an infinite universe).

 

[mabus]

A universe with a center is not a popular notion, but it cannot be ruled out. As I mentioned in an earlier post, I believe the popularization of the "no center" belief originated from the desire to establish that the BB was not an explosion that radially expelled matter, but rather was the homogeneous expansion of the universe from a single point. It quickly evolved into the widely held belief that there is no center. There is safety in following the pack, and the scientific community is not immune. This behavior is most certainly evident in this forum.
Here is an article about Lemaître that you should find enlightening.

http://math.ucr.edu/home/baez/physics/R ... entre.html

Actually it's more than a mere popular notion, it is an observed fact. The universe not having a center can be shown by simply pointing telescopes out towards the stars and galaxies and measuring their speed and direction. One can easily show that they are (over the whole) moving away from each other in every direction. They are not moving away from a central point. What you want to reduce to a mere "popular notion" is actually an experimentally validated observation.

Furthermore, It is mathematically true and remains a fundamental underpinning of Einstein's theory of Relativity which itself frames the Big Bang model. Saying it is a "mere popular notion" is rather unjustified when you consider it all carefully.

I would like to point out yet again, there is not a single authoratative scientific site (I am not talking about personal web pages from students at universities or blogs), claiming the universe is either bounded, or has a center. There is, I think a good reason for this.

 

[FlatEarth]

@ SpeedFreek.
I did not realize you posted it, otherwise I would have given you credit despite our differences.

I find it interesting that you come to a different conclusion after reading this article. Why is that? I show more of the article below to highlight the obvious –er- misunderstanding you have, and show how misleading your comments are.

from: http://math.ucr.edu/home/baez/physics/R ... entre.html
…The observable part is very large, but it is probably very small compared to the whole universe, which may even be infinite. We have no way of knowing what the shape of the universe is beyond the observable horizon, and no way of knowing whether the cosmological principle has any validity on the largest distance scales possible.
In 1927 Georges Lemaître found solutions of Einstein's equations of general relativity in which space expands. He went on to propose the Big Bang theory with those solutions as a model of the expanding universe. The best known class of solutions that Lemaître looked at were the homogeneous solutions now known as the Friedman-Lemaitre-Robertson-Walker (FLRW) models. (Friedmann found the solutions first but did not think of them as reasonable physical models). It is less well known that Lemaître found a more general class of solutions that describe a spherically symmetric expanding universe. These solutions, now known as Lemaître-Tolman-Bondi (LTB) models, describe possible forms for a universe that could have a centre. Since the FLWR models are actually a special limiting case of the LTB models, we have no sure way of knowing that the LTB models are not correct. The FLWR models may just be good approximations that work well within the limits of the observable universe but not beyond.

The article clearly states that the universe could have a center. It also states that Lemaître and his colleagues came up with the “spherically symmetric expanding universe” models. :!: This is what I have been saying all along!

(continued) Of course there are many other even less uniform shapes the universe could have, with or without an identifiable centre. If it turned out to have a centre on some scale beyond the observable universe, such a centre might turn out to be just one of many "centres" on much larger scales, just as the centre of our galaxy did before.
In other words, although the standard Big Bang models describe an expanding universe with no centre, and this is consistent with all observations, there is still a possibility that these models are not accurate on scales larger than we can observe. We still have no real answer to the question "Where is the centre of the universe?".

It is obvious the universe is bigger than we can see, so such a requirement is not a leap into fantasy. A multiple center scenario is another story, because there is no evidence for such a universe.

But there is a caveat here - as the link says:
"If it turned out to have a centre on some scale beyond the observable universe, such a centre might turn out to be just one of many "centres""

That is not a caveat. The definition of caveat is “an explanation to prevent misinterpretation”. This is stated as an alternate possibility, and clearly not a certain result of such a discovery. You either don’t understand the meaning of the word, or you are deliberately trying to mislead.

Are you now speculating outside the standard BB models and outside of the observable universe? If so, this is exactly what you accused me of earlier in this thread.

How can you ask such a ridiculous question? I cite the same shape of the universe that the man who created the BB theory proposed, and you say it is outside the theory? :roll:

Check, please. I’m ready to leave.

 

[FlatEarth]

A universe with a center is not a popular notion, but it cannot be ruled out. As I mentioned in an earlier post, I believe the popularization of the "no center" belief originated from the desire to establish that the BB was not an explosion that radially expelled matter, but rather was the homogeneous expansion of the universe from a single point. It quickly evolved into the widely held belief that there is no center. There is safety in following the pack, and the scientific community is not immune. This behavior is most certainly evident in this forum.
Here is an article about Lemaître that you should find enlightening.

http://math.ucr.edu/home/baez/physics/R ... entre.html

Actually it's more than a mere popular notion, it is an observed fact. The universe not having a center can be shown by simply pointing telescopes out towards the stars and galaxies and measuring their speed and direction. One can easily show that they are (over the whole) moving away from each other in every direction. They are not moving away from a central point. What you want to reduce to a mere "popular notion" is actually an experimentally validated observation.

Observations indicate a homogeneous, equally expanding universe, but by no means allow us to conclude as fact that there is no center. The jury is still out. Anyway, I am not proposing that everything exploded out of a central point. I made that very clear.

Furthermore, It is mathematically true and remains a fundamental underpinning of Einstein's theory of Relativity which itself frames the Big Bang model. Saying it is a "mere popular notion" is rather unjustified when you consider it all carefully.

If you mean that the theory of the expansion of the universe is based on General Relativity and is mathematically correct, then we agree on that point. If you are also saying that the math says there is no center, then I don't agree. Math will not tell us that.

It's tough to find any site that deals with the original, un-hijacked theory. The one I posted (and as it turns out SF also), was the best one out there so far. Universities are careful about what they allow to be associated with their names, so I trust it is accurate.

I am done with this topic. There is no point in arguing about this subject further.

 

[nimbus]

Paging Dr Rocket....

 

[ssnozenoszka]

No you are just being a contrarian. There are hundreds of sites on the internet that duscuss astronomy. Your library is full of books on astronomy. You local community college probably has astronomy courses. If you are truly eager to understand then use these resources. I do not feel like presenting evidence and have you disregared it. You state clearly in the first sentence that your mind is made up. Why waste my time?

Dear Origin,

Why have any discussions on internet at all when people should just go to the library or their local community college?

If what I ask is so simply provable then why do you not just supply some evidence? I was trying to have an argument based on ideas. It is obvious you are not capable of it, which is a shame. I am not a contrarian (as you so eloquently put it) at all. I just like to think outside of the box and go from simple to more complex (and abstract) explanations.

I read as an argument that everything seems to be moving away from everything else. Well DUH I would say, space itself is expanding what do you expect? That doesn't mean that that is the only mechanism at work, it means that is the most dominant mechanism, and thus the one most easily observable by us.

We look into the universe with a significant blur caused by our lacking theories and the limitations of our optical equipment. The truth is in the details, and we're just not seeing the details yet.

That is also why I said that pictures TAKEN a million years ago would be very interesting to have. Then we could compare how far galaxies have moved in those million years.

I hope there is someone else who is participating in this discussion that can shoot at my (very simple) earlier presented idea. What observations falsify this idea?

Kind regards,

S

 

[hvargas]

At one time it was the EARTH the center and now for 21th century science they will like to say that the Milky Way is the center of the Universe. This is not science, is speculations with nothing to logically explain it or to even theorize. I once say that if we were to go to the furthest galaxy from that galaxy we will focus an area and find that to a much greater distance more galaxies and if we go to such galaxies and look from there much further there will be even more galaxies much further away. Now imagine the age of the Universe as you find more ane more galaxies by such a method, there is no age to Space and there is no Time nor such a thing as SpaceTime. Time is a measurement of our existence but not a measurement to Space alone. There is no Center to Space but in order to demonstrate the BBT and to feed it with more evidence some want to create a Center to the Universe which will be t=0.

 

[SpeedFreek]

@ SpeedFreek.
I did not realize you posted it, otherwise I would have given you credit despite our differences.

I find it interesting that you come to a different conclusion after reading this article. Why is that? I show more of the article below to highlight the obvious –er- misunderstanding you have, and show how misleading your comments are.

from: http://math.ucr.edu/home/baez/physics/R ... entre.html
…The observable part is very large, but it is probably very small compared to the whole universe, which may even be infinite. We have no way of knowing what the shape of the universe is beyond the observable horizon, and no way of knowing whether the cosmological principle has any validity on the largest distance scales possible.
In 1927 Georges Lemaître found solutions of Einstein's equations of general relativity in which space expands. He went on to propose the Big Bang theory with those solutions as a model of the expanding universe. The best known class of solutions that Lemaître looked at were the homogeneous solutions now known as the Friedman-Lemaitre-Robertson-Walker (FLRW) models. (Friedmann found the solutions first but did not think of them as reasonable physical models). It is less well known that Lemaître found a more general class of solutions that describe a spherically symmetric expanding universe. These solutions, now known as Lemaître-Tolman-Bondi (LTB) models, describe possible forms for a universe that could have a centre. Since the FLWR models are actually a special limiting case of the LTB models, we have no sure way of knowing that the LTB models are not correct. The FLWR models may just be good approximations that work well within the limits of the observable universe but not beyond.

The article clearly states that the universe could have a center. It also states that Lemaître and his colleagues came up with the “spherically symmetric expanding universe” models. :!: This is what I have been saying all along!

I posted it on page 5. The first sentence in that quote says the universe might even be infinite, which I stated on page 1, post 5, and you were arguing against from post 6 onwards.

Just above the section you bolded it says that the FLRW solutions are homogeneous. The LTB models are not homogeneous. Standard Big Bang theory uses an FLRW homogeneous model, so any model with a centre is not part of standard Big Bang theory. You were claiming your logical conclusions for a finite universe with a centre were based on standard Big Bang theory, when they were not. If you had mentioned the LTB model at the outset we might have avoided this mess, but you kept saying you were using standard BB theory, when you were not. This is why mabus was trying to pin you down as to the definitions you were using, I should have noticed that.

When I suggested an infinite universe you claimed I was "outside" of Big Bang theory, and that the BB defines the universe as being finite, which it does not. The quote below illustrates what I mean.

The post where you state "The Big Bang states that our observable part of the universe started off very small, but the universe as a whole might have been any size at that time." is the one I argue against. The "universe as a whole" implies a greater universe than the one produced by the BB.

As I said earlier, the universe as a whole might have been infinite to begin with, but it was all produced in the BB. You seemed to be arguing that only the observable universe was produced by the BB.

In my post on page 5 I said "There is just as much chance that the universe is infinite as there is that it is finite." You addressed this in the next post with the statement:

When Wright says "Whereof one cannot speak, thereof one must be silent." he apparently would agree with my position. Let's speak of the universe we know of, for even though there may be others, they are just in our collective imagination at this time. My logic is indeed based on the BB theory, and not on a fanciful, unsupported multiple universe theory.

Wright was referring to questions about "before the Big Bang", he is quite prepared to speak of an infinite universe. So, in my view, you were incorrectly continuing to confuse an infinite Big Bang universe (part of standard BB) with some sort of multiple universe theory, just as you did on page 1 post 6. You might have been talking about Wrights "bubble universes", but if you look you will see you were replying to my statement about our universe possibly being infinite in extent.

(continued) Of course there are many other even less uniform shapes the universe could have, with or without an identifiable centre. If it turned out to have a centre on some scale beyond the observable universe, such a centre might turn out to be just one of many "centres" on much larger scales, just as the centre of our galaxy did before.
In other words, although the standard Big Bang models describe an expanding universe with no centre, and this is consistent with all observations, there is still a possibility that these models are not accurate on scales larger than we can observe. We still have no real answer to the question "Where is the centre of the universe?".

It is obvious the universe is bigger than we can see, so such a requirement is not a leap into fantasy. A multiple center scenario is another story, because there is no evidence for such a universe.

The start of the second paragraph states that standard Big Bang models describe an expanding universe with no centre. The LTB model is not a standard Big Bang model and I have been arguing with you all along because you claimed your logical conclusions are based in the standard Big Bang model when they most certainly are not!

Lemaître (which is the "L" in the FLRW solution) may have also proposed a universe with a centre, but that is not part of the homogeneous FLRW solution that is used in standard Big Bang theory, which is the theory you seemed to be claiming you were applying your logic to.

Are you now speculating outside the standard BB models and outside of the observable universe? If so, this is exactly what you accused me of earlier in this thread.

How can you ask such a ridiculous question? I cite the same shape of the universe that the man who created the BB theory proposed, and you say it is outside the theory? :roll:

Check, please. I’m ready to leave.

I thought you said "Let's speak of the universe we know of". The LTB theory is not standard Big Bang theory, it is a generalised solution to the EFE that does not seem to apply to our observable universe, which is homogeneous at the largest observed scales.

All I have been arguing with you about is your claim that you are applying logic to the standard Big Bang model. You claimed that, since there was no space or time before the Big Bang, that the universe must be finite and therefore have a centre.

I replied that the universe might be infinite, and this thread went downhill from there, as you argued that I was invoking multiple universe theories etc, when I was simply applying standard BB theory, as shown above.

If you re-read this thread (starting from page 1) you will see what I mean. Perhaps we have been talking past each other all along (I asked if this was the case on page 1, also).

I most certainly do understand BB theory but the wording of your posts made it seem to me that you did not. I am guessing the same can be said the other way round, eh?



(If DrRocket were here, he would be slapping us both and telling us that this is why people need to show the math when discussing these issues, as it helps avoid exactly these kinds of situations! In case anyone is wondering, he now posts over at BAUT, which is better suited to his rigorous nature!)

 

[mabus]

Observations indicate a homogeneous, equally expanding universe, but by no means allow us to conclude as fact that there is no center. The jury is still out.

Why the bloody hell not? Are you saying relativity is wrong and that, rather than position and velocity being relative to another that they are all relative to an absolute central point? If so, then every major university department on the planet, and every noted physicist is wrong. Shall I notify the nobel committee or will you handle it?

Furthermore, It is mathematically true and remains a fundamental underpinning of Einstein's theory of Relativity which itself frames the Big Bang model. Saying it is a "mere popular notion" is rather unjustified when you consider it all carefully.

If you mean that the theory of the expansion of the universe is based on General Relativity and is mathematically correct, then we agree on that point. If you are also saying that the math says there is no center, then I don't agree. Math will not tell us that.

It's tough to find any site that deals with the original, un-hijacked theory. The one I posted (and as it turns out SF also), was the best one out there so far. Universities are careful about what they allow to be associated with their names, so I trust it is accurate.

Your claim that this page supports your position, that believing the universe has a center is a logical conclusion, reached from the BB model stems from the paragraph at the bottom of the page in question.

In other words, although the standard Big Bang models describe an expanding universe with no centre, and this is consistent with all observations, there is still a possibility that these models are not accurate on scales larger than we can observe. We still have no real answer to the question "Where is the centre of the universe?".

He is correct when he says the universe COULD have a center. It very well might. If our models inaccurately describe the universe at larger scales than we can presently observe, then it very well may be that it does have a center, just as our ability to observe the universe beyond our galaxy allowed us to refine older less accurate models of the universe which viewed the milky way as the entire static non-expanding universe.

The problem is, you're not claiming that it's possible that, although the BB model says there is no center, that there could hypothetically still be one. You're claiming that a center of the universe is a LOGICAL CONCLUSION from the BB model. Something your own source here rejects, clearly writting

although the standard Big Bang model describes an expanding universe with no center and this is consistant with ALL observations

This is in fact quite the opposite of what you are claiming

 

[SpeedFreek]

Heh. I should point out, as I was the one that first posted that link, that John Baez is actually a renowned mathematical physicist and is Professor of Mathematics at UCR. So we can assume that his department at the university will have approved his texts, as he is the head of that department!

 

[mabus]

Ah ok, I wasn't aware of that. I've amended my post to reflect the information.